1. Field of the Invention
The present invention relates to a sheet feeding apparatus and an image forming apparatus, and particularly relates to a configuration for lifting and lowering a sheet stacking portion which stacks a sheet.
2. Description of the Related Art
A related art image forming apparatus such as a printer, a duplicator, or a facsimile machine has a sheet feeding apparatus which delivers a sheet stored in a sheet storage portion, which is provided detachably in the image forming apparatus body, by a sheet feeding unit to be fed to an image forming portion. An example of the sheet feeding apparatus is provided with a sheet stacking portion in the sheet storage portion to be lifted and lowered, and the sheet stacking portion is lifted when feeding a sheet to press the sheet against the sheet feeding unit thereby feeding the sheet. In the sheet feeding apparatus, the sheet stacking portion is lifted according to the sheet stacking amount by a lifter mechanism that is a lifting and lowing mechanism in order to keep the height of the uppermost sheet to a predetermined height at which sheet feeding is possible.
The image forming apparatus body is provided with a driving unit having a gear and a motor which drives the gear to drive the lifter mechanism, and when the sheet storage portion is mounted, the lifter mechanism is connected to the driving unit. Note that, when a user feeds a sheet or changes the kind of sheet, or sheet jam is occurred, the sheet storage portion is extracted from the image forming apparatus body so that the connection between the lifter mechanism and the driving unit is released. The sheet stacking portion is lowered when the connection is released.
FIG. 7 illustrates a configuration of this related art sheet feeding apparatus. A lifter gear 135 is connected via a lifter shaft 134 to a lifter plate 133 which lifts and lowers a sheet supporting plate 132 which is rotatably provided inside a sheet feeding cassette 130 about a fulcrum 132a. Then, when the sheet feeding cassette 130 is mounted, the lifter gear 135 is connected to a driving unit 144 having lifter idler gears 141, 142 and a lifter motor 143 provided to the image forming apparatus body (not illustrated). Thereby, when the lifter motor 143 is rotated, the lifter gear 135 meshed with the lifter idler gear 141 is rotated, and thereby the sheet supporting plate 132 is lifted via the lifter shaft 134.
In the related art, a sheet storage portion is required to enlarge capacity and deal with various sheets with high density. On the other hand, however, it also needs to satisfy a proposition called thinning, miniaturization and weight reduction aiming cost reduction. Further, in the lifter mechanism and the driving unit, it is required to improve reliability upon drive transmission against increase in the maximum number of stacked sheets and a load increased according to a request to feed a sheet with a large basis weight.
Therefore, in a the related sheet feeding apparatus, the lifter idler gears 141, 142 and the lifter gear 135 illustrated in FIG. 8A are high module gears with high rigidity respectively (see Japanese Patent Laid-Open No. 2003-246468). Additionally, as illustrated in FIG. 8B, there is a sheet feeding apparatus in which a boss 136 is provided to a sheet feeding cassette 131 and also an opening portion 145 is provided to a frame 146 of the image forming apparatus body. There, the boss 136 is engaged with the opening portion 145 near the lifter idler gears 141, 142 and the lifter gear 135 and also outside of a rotation range K of the lifter gear 135 so that the gears are properly meshed with each other at a high load as well (see Japanese Patent Laid-Open No. 2004-123308).
However, in such a related art sheet feeding apparatus, even when the lifter idler gears and the lifter gear are high module gears, the frame 146 and the lifter shaft 134 supporting them are sometimes deformed at a high load. Especially, in a product from which weight and thickness are reduced, there is a risk that the lifter shaft 134 is inclined in the width direction orthogonal to the sheet feeding direction or bent downward at a high load, and thereby proper meshing between the gears may be impaired.
And also, in a configuration that the boss 136 is engaged with the frame 146, the opening portion 145 needs to be formed outside of the rotation range K of the lifter gear 135. However, a location in which the boss 136 and the opening portion 145 are formed may be restricted due to a configuration of the frame 146 or the sheet feeding cassette 131. Therefore, reliability of meshing between the gears needs to be ensured with an additional cost for metalizing the lifter shaft 134 and the frame.
Then, the present invention is made considering such a situation so as to provide a sheet feeding apparatus and an image forming apparatus capable of ensuring reliability of meshing between gears at low cost.